This invention relates to master cylinder assemblies and more particularly to dual master cylinder assemblies suitable for use, for example, in motor vehicle braking systems.
It has become common practice in recent years for motor vehicles to employ braking systems in which two of the wheels are on one braking circuit and the other two wheels are on a second braking circuit so that failure of one circuit will not totally destroy the braking capacity of the vehicle. This dual circuit arrangement has necessitated master cylinders employing two separate pistons which separately provide pressurized fluid to the two circuits of the vehicle braking system. It is also common practice to provide some means for determining when a failure has occurred in either braking circuit and apprising the vehicle operator of such failure. In one popular prior art warning system, a shuttle member is placed in communication at its opposite ends with the two pressure chambers associated with the two pistons of the master cylinder so that the shuttle member is moved axially in response to a significant difference in the pressures in the two pressure chambers and this movement of the shuttle member is sensed to provide a warning signal indicating that one of the brake circuits has failed. Whereas this prior art warning system has been generally satisfactory in the sense of providing a warning of brake system failure, the system requires violation of the bore of the cylinder with the consequent creation of fluid leakage paths in the master cylinder assembly; the system requires seals so that the hydraulic pressure fluid employed to move the shuttle member does not escape from the system; the system requires an expensive failure switch to sense the movement of the shuttle member; and the system requires several intricate machining operations with respect to the associated master cylinder assembly to provide the required structure and fluid paths for the warning system.